Patent application title: SETTING INSPIRATORY TIME IN MANDATORY MECHANICAL VENTILATION BASED ON PATIENT PHYSIOLOGY, SUCH AS WHEN TIDAL VOLUME IS INSPIRED

Abstract:

A method of setting inspiratory time in pressure controlled mechanical
ventilation sets a subject's inspiratory time based on when the subject's
tidal volume is inspired. Another determines when the subject's tidal
volume is inspired and sets the subject's inspiratory time based on the
determination.

Claims:

1. A method of setting inspiratory time in pressure controlled mechanical
ventilation, comprising:setting a subject's inspiratory time based on
when said subject's tidal volume is inspired.

2. A method of setting inspiratory time in pressure controlled mechanical
ventilation, comprising:determining when a subject's tidal volume is
inspired; andsetting said subject's inspiratory time based on said
determination.

3. The method of claim 2, wherein said inspiratory time is set equal to
when said tidal volume is inspired.

4. The method of claim 2, wherein said inspiratory time is set
substantially equal to when said tidal volume is inspired.

5. The method of claim 2, wherein said inspiratory time is set greater
than or equal to when said tidal volume is inspired.

6. The method of claim 2, wherein said determination is based, at least in
part, on a flow rate sensor.

7. The method of claim 6, wherein said flow rate sensor is selected from a
group consisting of a spirometer, anemometer, thermal anemometer,
pneumotachometer, and ultrasound flow sensor.

9. The method of claim 2, wherein said determination is based, at least in
part, on effects of gas movement in said subject's airways.

10. The method of claim 9, wherein said effects are determined, at least
in part airway pressure analysis of said subject.

11. The method of claim 2, wherein said determination is based, at least
in part, on thoracic excursion of said subject corresponding to said
subject's lung volume.

12. The method of claim 11, wherein said thoracic excursion comprises one
or more of the following:imaging said subject;plethysmographic analysis
of said subject; andelectrical impedance tomography analysis of said
subject.

13. The method of claim 2, further comprising:displaying at least one or
more of when said tidal volume is inspired or said inspiratory time or
both on a monitor.

14. The method of claim 13, wherein said monitor is at least one of a
handheld or portable device or both.

15. A device for use in pressure controlled mechanical ventilation,
comprising:a flow rate sensor configured to determine when a subject's
tidal volume is inspired and base said subject's inspiratory time on said
determination.

16. The device of claim 15, wherein said flow rate sensor is selected from
a group consisting of a spirometer, anemometer, thermal anemometer,
pneumotachometer, and ultrasound flow sensor.

18. The device of claim 15, further comprising:circuitry operable in
conjunction with said flow rate sensor configured to set said inspiratory
time based on said determination.

Description:

FIELD OF INVENTION

[0001]In general, the inventive arrangements relate to respiratory care,
and more specifically, to improvements in controlling mandatory
mechanical ventilation.

BACKGROUND OF INVENTION

[0002]Referring generally, when patients are medically unable to breathe
on their own, mechanical, or forced, ventilators can sustain life by
providing requisite pulmonary gas exchanges on behalf of the patients.
Accordingly, modern ventilators usually include electronic and pneumatic
control systems that control the pressure, flow rates, and/or volume of
gases delivered to, and extracted from, patients needing medical
respiratory assistance. Oftentimes, such control systems include a
variety of knobs, dials, switches, and the like, for interfacing with
treating clinicians, who support the patient's breathing by adjusting the
afore-mentioned pressure, flow rates, and/or volume of the patient's
pulmonary gas exchanges, particularly as the condition and/or status of
the patient changes. Even today, however, such parameter adjustments,
although highly desirable, remain challenging to control accurately,
particularly using present-day arrangements and practices.

[0003]Referring now more specifically, ventilation is a complex process of
delivering oxygen to, and removing carbon dioxide from, alveoli within
patients' lungs. Thus, whenever a patient is ventilated, that patient
becomes part of a complex, interactive system that is expected to promote
adequate ventilation and gas exchange on behalf of the patient,
eventually leading to the patient's stabilization, recovery, and ultimate
ability to return to breathing normally and independently.

[0004]Not surprisingly, a wide variety of mechanical ventilators are
available today. Most allow their operating clinicians to select and use
several modes of ventilation, either individually and/or in various
combinations, using various ventilator setting controls.

[0005]These mechanical ventilation modes are generally classified into one
(1) of two (2) broad categories: a) patient-triggered ventilation, and b)
machine-triggered ventilation, the latter of which is also commonly
referred to as controlled mechanical ventilation (CMV). In
patient-triggered ventilation, the patient determines some or all of the
timing of the ventilation parameters, while in CMV, the operating
clinician determines all of the timing of the ventilation parameters.
Notably, the inventive arrangements described hereinout will be
particularly relevant to CMV.

[0006]In recent years, mechanical ventilators have become increasingly
sophisticated and complex, due, in large part, to recently-enhanced
understandings of lung pathophysiology. Technology also continues to play
a vital role. For example, many modern ventilators are now
microprocessor-based and equipped with sensors that monitor patient
pressure, flow rates, and/or volumes of gases, and then drive automated
responses in response thereto. As a result, the ability to accurately
sense and transduce, combined with computer technology, makes the
interaction between clinicians, ventilators, and patients more effective
than ever before.

[0007]Unfortunately, however, as ventilators become more complicated and
offer more options, the number and risk of potentially dangerous clinical
decisions increases as well. Thus, clinicians are often faced with
expensive, sophisticated machines, yet few follow clear, concise, and/or
consistent guidelines for maximal use thereof. As a result, setting,
monitoring, and interpreting ventilator parameters can devolve into
empirical judgment, leading to less than optimal treatment, even by
well-intended practitioners.

[0008]Complicating matters ever further, ventilator support should be
individually tailored for each patient's existing pathophysiology, rather
than deploying a generalized approach for all patients with potentially
disparate ventilation needs.

[0009]Pragmatically, the overall effectiveness of assisted ventilation
will continue to ultimately depend on mechanical, technical, and
physiological factors, with the clinician-ventilator-patient interface
invariably continuing to play a key role. Accordingly, technology that
demystifies these complex interactions and provides appropriate
information to effectively ventilate patients is needed.

[0011]In one embodiment, a method of setting inspiratory time in pressure
controlled mechanical ventilation sets a subject's inspiratory time based
on when the subject's tidal volume is inspired.

[0012]In another embodiment, a method of setting inspiratory time in
pressure controlled mechanical ventilation determines when a subject's
tidal volume is inspired and sets the subject's inspiratory time based on
the determination.

[0013]In yet another embodiment, a device for use in pressure controlled
mechanical ventilation comprises a flow rate sensor configured to
determine when a subject's tidal volume is inspired and base the
subject's inspiratory time on the determination.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0014]A clear conception of the advantages and features constituting
inventive arrangements, and of various construction and operational
aspects of typical mechanisms provided by such arrangements, are readily
apparent by referring to the following illustrative, exemplary,
representative, and/or non-limiting figures, which form an integral part
of this specification, in which like numerals generally designate the
same elements in the several views, and in which:

[0015]FIG. 1 depicts a front perspective view of a medical system
comprising a ventilator;

[0016]FIG. 2 depicts a block diagram of a medical system providing
ventilator support to a patient;

[0017]FIG. 3 depicts a block diagram of a ventilator providing ventilator
support to the patient;

[0018]FIG. 4 depicts a flow diagram of the patient's inspiratory time
(TI), expiratory time (TE), and forced inhalation time
(TINH) for a single breath, particularly during pressure controlled
mechanical ventilation (CMV);

[0019]FIG. 5 depicts a flowchart of a simplified arrangement for setting
the patient's inspiratory time (TI) based on the patient's forced
inhalation time (TINH);

[0020]FIG. 6 depicts a flowchart of a simplified arrangement for setting
the patient's inspiratory time (TI) based on when the patient's
forced inhalation flow ceases;

[0021]FIG. 7 depicts a flowchart of a simplified arrangement for setting
the patient's inspiratory time (TI) based on when the patient's
tidal volume is inspired;

[0025]Referring now to the figures, and in particular to FIGS. 1-3, a
medical system 10 is depicted for mechanically ventilating a patient 12.
More specifically, an anesthesia machine 14 includes a ventilator 16, the
latter having suitable connectors 18, 20 for connecting to an inspiratory
branch 22 and expiratory branch 24 of a breathing circuit 26 leading to
the patient 12. As will be subsequently elaborated upon, the ventilator
16 and breathing circuit 26 cooperate to provide breathing gases to the
patient 12 via the inspiratory branch 22 and to receive gases expired by
the patient 12 via the expiratory branch 24.

[0026]If desired, the ventilator 16 can also be provided with a bag 28 for
manually bagging the patient 12. More specifically, the bag 28 can be
filled with breathing gases and manually squeezed by a clinician (not
shown) to provide appropriate breathing gases to the patient 12. Using
this bag 28, or "bagging the patient," is often required and/or preferred
by the clinicians, as it can enable them to manually and/or immediately
control delivery of the breathing gases to the patient 12. Equally
important, the clinician can sense conditions in the respiration and/or
lungs 30 of the patient 12 according to the feel of the bag 28, and then
accommodate for the same. While it can be difficult to accurately obtain
this feedback while mechanically ventilating the patient 12 using the
ventilator 16, it can also fatigue the clinician if the clinician is
forced to bag the patient 12 for too long a period of time. Thus, the
ventilator 16 can also provide a toggle 32 for switching and/or
alternating between manual and automated ventilation.

[0028]Referring now more specifically to FIG. 2, the ventilator 16
provides breathing gases to the patient 12 via the breathing circuit 26.
Accordingly, the breathing circuit 26 typically includes the
afore-mentioned inspiratory branch 22 and expiratory branch 24. Commonly,
one end of each of the inspiratory branch 22 and expiratory branch 24 is
connected to the ventilator 16, while the other ends thereof are usually
connected to a Y-connector 40, which can then connect to the patient 12
through a patient branch 42, which can also include an interface 43 to
secure the patient's 12 airways to the breathing circuit 26 and/or
prevent gas leakage out thereof.

[0029]Referring now more specifically to FIG. 3, the ventilator 16 can
also include electronic control circuitry 44 and/or pneumatic circuitry
46. More specifically, various pneumatic elements of the pneumatic
circuitry 46 provide breathing gases to the lungs 30 of the patient 12
through the inspiratory branch 22 of the breathing circuit 26 during
inhalation. Upon exhalation, the breathing gases are discharged from the
lungs 30 of the patient 12 and into the expiratory branch 24 of the
breathing circuit 26. This process can be iteratively enabled by the
electronic control circuitry 44 and/or pneumatic circuitry 46 in the
ventilator 16, which can establish various control parameters, such as
the number of breaths per minute to administer to the patient 12, tidal
volumes (VT), maximum pressures, etc., that can characterize the
mechanical ventilation that the ventilator 16 supplies to the patient 12.
As such, the ventilator 16 may be microprocessor based and operable in
conjunction with a suitable memory to control the pulmonary gas exchanges
in the breathing circuit 26 connected to, and between, the patient 12 and
ventilator 16.

[0030]Even more specifically, the various pneumatic elements of the
pneumatic circuitry 46 usually comprise a source of pressurized gas (not
shown), which can operate through a gas concentration subsystem (not
shown) to provide the breathing gases to the lungs 30 of the patient 12.
This pneumatic circuitry 46 may provide the breathing gases directly to
the lungs 30 of the patient 12, as typical in a chronic and/or critical
care application, or it may provide a driving gas to compress a bellows
48 (see FIG. 1) containing the breathing gases, which can, in turn,
supply the breathing gases to the lungs 30 of the patient 12, as typical
in an anesthesia application. In either event, the breathing gases
iteratively pass from the inspiratory branch 22 to the Y-connector 40 and
to the patient 12, and then back to the ventilator 16 via the Y-connector
40 and expiratory branch 24.

[0031]In the embodiment depicted in FIG. 3, one or more of the sensors 34,
placed in the breathing circuit 26, can also provide feedback signals
back to the electronic control circuitry 44 of the ventilator 16,
particularly via a feedback loop 52. More specifically, a signal in the
feedback loop 52 could be proportional, for example, to gas flows and/or
airway pressures in the patient branch 42 leading to the lungs 30 of the
patient 12. Inhaled and exhaled gas concentrations (such as, for example,
oxygen O2, carbon dioxide CO2, nitrous oxide N2O, and
inhalation anesthetic agents), flow rates (including, for example,
spirometry), and gas pressurization levels, etc., are also representative
feedback signals that could be captured by the sensors 34, as can the
time periods between when the ventilator 16 permits the patient 12 to
inhale and exhale, as well as when the patient's 12 natural inspiratory
and expiratory flows cease.

[0032]Accordingly, the electronic control circuitry 44 of the ventilator
16 can also control displaying numerical and/or graphical information
from the breathing circuit 26 on the monitor 38 of the medical system 10
(see FIG. 1), as well as other patient 12 and/or system 10 parameters
from other sensors 34 and/or the processing terminal 36 (see FIG. 1). In
other embodiments, various components of which can also be integrated
and/or separated, as needed and/or desired.

[0033]By techniques known in the art, the electronic control circuitry 44
can also coordinate and/or control, among other things, for example,
other ventilator setting signals 54, ventilator control signals 56,
and/or a processing subsystem 58, such as for receiving and processing
signals, such as from the sensors 34, display signals for the monitor 38
and/or the like, alarms 60, and/or an operator interface 62, which can
include one or more input devices 64, etc., all as needed and/or desired
and interconnected appropriately (e.g., see FIG. 2). These components are
functionally depicted for clarity, wherein various ones thereof can also
be integrated and/or separated, as needed and/or desired. For further
enhanced clarity, other functional components should also be
well-understood but are not shown--e.g., one or more power supplies for
the medical system 10 and/or anesthesia machine 14 and/or ventilator 16,
etc. (not shown).

[0034]Now then, against this background, the inventive arrangements
establish ventilation parameters according to patient physiology. These
arrangements, to be now described, allow clinicians to control patient
ventilation parameters throughout the patient's 12 respiratory cycle and
enables ventilation treatments to be individually optimized for patients
12 subject to pressure controlled mechanical ventilation (CMV).

[0035]Referring generally, pressure controlled mechanical ventilation
(CMV) consists of a decelerating inspiratory gas flow, for example as
resulting from a pressure controlled ventilation (PCV) mode whereby flow
ceases when the patient's 12 inflated lung pressure equilibrates with the
inspired pressure (PINSP), which can be a user settable parameter in
PCV ventilation mode. Such a decelerating flow pattern can also be
experienced when a ventilator 16 delivers a predetermined short volume
pulse into a breathing circuit 26 and allows the gas pressure in the
breathing circuit 26 to equilibrate within the patient's 12 lungs 30.
When pressure equilibration occurs between the breathing circuit 26 and
the patient's 12 lungs 30, inspiratory flow ceases. One can also
appreciate that during the inspiratory phase of ventilation, there are
other ventilator flow patterns that can rapidly force an anticipated gas
volume by initially delivering a high ventilator flow followed by a flow
reduction to zero or nearly zero flow. In response to this forced
inhalation, gas flow to the patient's 12 lungs 30 decelerates to zero or
near zero when the desired tidal volume (VT) is attained. Hereinout,
these ventilator control methods are included as representative pressure
controlled ventilation (PCV). In particular, pressure controlled
ventilation (PCV) has delivers the tidal gas volume VT to the
patient 12 over a generally shorter time than a constant flow volume
control ventilation (VCV) mode. In VCV, for example, the ventilator 16
delivers a constant flow over the entire set inspiratory times
(sTI). The early delivery of the entire tidal gas volume VT in
PCV verses VCV allows more gases in the patient's 12 lungs 30 to exchange
with the patient's 12 pulmonary blood early in the inspiratory phase of
ventilation, making PCV generally more efficient in removing or adding
gases into the patient's 12 blood than VCV. This is particularly evident
for a patient 12 who is being ventilated at high respiration rate or for
gases that diffuse more slowly through the patient's 12 alveolar to the
patient's 12 blood.

[0036]To facilitate the following discussion, the following generalized
and/or representative explanations and/or definitions may be referred to:

[0037]1. TI is Inspiratory Time.

[0038]More specifically, TI is the amount of time, measured in
seconds, set on the ventilator 16 by the clinician, lasting from the
beginning of the patient's 12 inspiration to the beginning of the
patient's 12 expiration. Accordingly, TI is the patient's 12
inspiratory time.

[0039]Inspiratory times TI can be further broken down into a set
inspiratory time sTI, a delivered inspiratory time dTI, and a
measured inspiratory time mTI. More specifically, the set
inspiratory time sTI is the amount of time that the clinician sets
on the ventilator 16 to deliver gases to the patient 12 during
inspiration, while the delivered inspiratory time dTI is the amount
of time that gases are actually allowed to be delivered to the patient 12
from the ventilator 16 during inspiration. Similarly, the measured
inspiratory time mTI is the amount of time that the ventilator 16
measures for allowing gases to be delivered to the patient 12 during
inspiration. Ideally, the set inspiratory time sTI, delivered
inspiratory time dTI, and measured inspiratory time mTI are
equal or substantially equal. However, if the clinician or ventilator 16
is searching for an optimal inspiratory time TI, as elaborated upon
below, then each of these inspiratory times TI may be different or
slightly different. For example, the clinician and/or ventilator 16 may
have established a set inspiratory time sTI, yet the delivered
inspiratory time dTI may deviate therefrom in the process of
searching for, for example, the patient's 12 forced inhalation time
TINH.

[0040]2. TE is Expiratory Time.

[0041]More specifically, TE is the amount of time, measured in
seconds, set on the ventilator 16 by the clinician, lasting from the
beginning of the patient's 12 expiration to the beginning of the
patient's 12 inspiration. Accordingly, TE is the patient's 12
expiratory time.

[0042]Like inspiratory times TI, expiratory times TE can also be
further broken down into a set expiratory time sTE, a delivered
expiratory time dTE, and a measured expiratory time mTE. More
specifically, the set expiratory time sTE is the amount of time that
the clinician sets on the ventilator 16 to allow the patient 12 to exhale
gases during expiration, while the delivered expiratory time dTE is
the amount of time that gases are allowed to be exhaled by the patient 12
during expiration. Similarly, the measured expiratory time mTE is
the amount of time that the ventilator 16 measures for having allowed the
patient 12 to exhale gases during expiration. Ideally, the set expiratory
time sTE, delivered expiratory time dTE, and measured
expiratory time mTE are equal or substantially equal. However, if
the clinician or ventilator 16 is searching for an optimal expiratory
time TE-OPTIMAL, as elaborated upon below, then each of these
expiratory times TE may be different or slightly different. For
example, the clinician and/or ventilator 16 may have established a set
expiratory time sTE, yet the delivered expiratory time dTE may
deviate therefrom in the process of searching, for example, for the
patient's 12 optimal expiratory time TE-OPTIMAL.

[0043]3. I:E Ratios are Ratios Between TI and TE.

[0044]More specifically, I:E ratios measure inspiratory times divided by
expiratory times--i.e., TI/TE, which is commonly expressed as a
ratio. Common I:E ratios are 1:2, meaning patients 12 may inhale for a
certain period of time (x) and then exhale for twice as long (2x).
However, since some patients 12 may have obstructed pathologies (e.g.,
chronic obstructive pulmonary disease (COPD)) and/or slower exhalation,
requiring the clinician to set longer expiratory times TE, I:E
ratios can also be set at ratios closer to 1:3 and/or 1:4, particularly
to provide the necessary expiratory time TE for a given patient 12
to fully exhale, although I:E ratios from 1:8 and 2:1 are also not
uncommon, with common ventilators 16 providing 0.5 gradations
therebetween.

[0045]4. TINH is Forced Inhalation Time.

[0046]More specifically, TINH is the amount of time, measured in
seconds, required for the patient's 12 forced inhalation flow to cease
during pressure controlled mechanical ventilation. Accordingly, TINH
is the patient's 12 forced inhalation time.

[0047]Oftentimes in pressure controlled mechanical ventilation, the
patient's 12 inspiratory time TI does not equal the patient's 12
forced inhalation time TINH--i.e., the patient's 12 inspiratory time
TI, as set by the clinician on the ventilator 16, often does not
coincide with the patient's 12 forced inhalation time TINH.
Moreover, in accordance with many default settings on many ventilators
16, respiratory rates f (see below) are commonly set between 6-10
breaths/minute and I:E ratios are commonly set at 1:2, resulting in many
clinicians setting inspiratory times TI between 2.0-3.3 seconds, as
opposed to typical inhalation times TINH being less than or equal to
approximately 0.8-1.5 seconds. Several of the inventive arrangements, on
the other hand, set the patient's 12 inspiratory times TI
approximately equal to the patient's 12 forced inhalation times TI
(i.e., 2*TINH≧TI≧TINH).

[0048]If the clinician or ventilator 16 sets the patient's 12 inspiratory
time TI less than or equal to the patient's 12 forced inhalation
time TINH, there can be inadequate time for the patient 12 to
inspire the gases in the patient's 12 lungs 30. This can result in
insufficient breath volume in the patient's 12 lungs 30, thereby
inadvertently and/or unknowingly under-ventilating the patient's 12 lungs
30. Accordingly, several of the inventive arrangements set the patient's
12 inspiratory time TI approximately equal to the patient's 12
forced inhalation time TINH, preferably with the patient's 12
inspiratory time TI being set greater than or equal to the patient's
12 force inhalation time TINH.

[0049]5. PEEP is Positive End Expiratory Pressure.

[0050]More specifically, PEEP is the patient's 12 positive end expiratory
pressure, often measured in cmH2O. Accordingly, PEEP is the amount
of pressure in the patient's 12 lungs 30 at the end of the patient's 12
expiratory time TE, as controlled by the ventilator 16.

[0051]Like inspiratory times TI and expiratory times TE,
positive end expiratory pressure PEEP can also be further broken down
into a set positive end expiratory pressure sPEEP, a measured positive
end expiratory pressure mPEEP, and a delivered positive end expiratory
pressure dPEEP. More specifically, the set positive end expiratory
pressure sPEEP is the amount of pressure that the clinician sets on the
ventilator 16 for the patient 12, while the measured positive end
expiratory pressure mPEEP is the amount of pressure in the patient's 12
lungs 30 at the end of the patient's 12 expiratory time TE.
Similarly, the delivered positive end expiratory pressure dPEEP is the
amount of pressure delivered by the ventilator to the patient 12.
Usually, the set positive end expiratory pressure sPEEP, measured
positive end expiratory pressure mPEEP, and delivered positive end
expiratory pressure dPEEP are equal or substantially equal. However, the
measured positive end expiratory pressure mPEEP can be greater than the
set positive end expiratory pressure sPEEP when breath stacking, for
example, occurs.

[0052]6. FIO2 is Fraction of Inspired Oxygen.

[0053]More specifically, FIO2 is the concentration of oxygen in
the patient's 12 inspiratory gas, often expressed as a fraction or
percentage. Accordingly, FIO2 is the patient's 12 fraction of
inspired oxygen.

[0054]7. FEO2 is Fraction of Expired Oxygen.

[0055]More specifically, FEO2 is the concentration of oxygen in
the patient's 12 expiratory gas, often expressed as a fraction or
percentage. Accordingly, FEO2 is the patient's 12 fraction of
expired oxygen.

[0056]8. f is Respiratory Rate.

[0057]More specifically, f is the patient's 12 respiratory rate, measured
in breaths/minute, set on the ventilator 16 by the clinician.

[0058]9. VT is Tidal Volume.

[0059]More specifically, VT is the total volume of gases, measured in
milliliters, delivered to the patient's 12 lungs 30 during inspiration.
Accordingly, VT is the patient's 12 tidal volume.

[0060]Like inspiratory times TI and expiratory times TE, tidal
volumes VT can also be further broken down into a set tidal volume
sVT, a delivered tidal volume dVT, and a measured tidal volume
mVT. More specifically, the set tidal volume sVT is the volume
of gases that the clinician sets on the ventilator 16 to deliver gases to
the patient 12 during inspiration, while the delivered tidal volume
dVT is the volume of gases actually delivered to the patient 12 from
the ventilator 16 during inspiration. Similarly, the measured tidal
volume mVT is the volume of gases that the ventilator 16 measures
for having delivered gases to the patient 12 during inspiration. Ideally,
the set tidal volume sVT, delivered tidal volume dVT, and
measured tidal volume mVT are equal or substantially equal. However,
if the clinician or ventilator 16 is searching for a set optimal tidal
volume sVT, as elaborated upon below, then each of these set tidal
volumes sVT may be different or slightly different.

[0061]10. FETCO2 is End Tidal Carbon Dioxide CO2.

[0062]More specifically, FETCO2 is the concentration of carbon
dioxide CO2 in the patient's 12 exhaled gas, often expressed as a
fraction or percentage. Accordingly, FETCO2 is the amount of
carbon dioxide CO2 exhaled by the patient 12 at the end of a given
breath.

[0063]11. VCO2 is the Volume of Carbon Dioxide CO2 per Breath.

[0064]More specifically, VCO2 is the volume of carbon dioxide
CO2 that the patient 12 exhales in a single breath. Accordingly,
VCO2 is the patient's 12 volume of CO2 exhaled per breath.

[0065]Now then, clinicians usually begin ventilation by selecting an
initial set tidal volume sVT, respiratory rate f, and I:E ratio. The
respiratory rate f and I:E ratio usually determine the initial set
inspiratory time sTI and initial set expiratory time sTE that
the clinician sets on the ventilator 16. In other words, the actual set
inspiratory time sTI and actual set expiratory time sTE that
the clinician uses are usually determined in accordance with the
following equations:

f = 60 sT I + sT E I : E = sT I sT E

[0066]Moreover, the clinician usually makes these initial determinations
based on generic rule-of-thumb settings, taking into account factors such
as, for example, the patient's 12 age, weight, height, gender,
geographical location, etc. Once the clinician makes these initial
determinations, the inventive arrangements can now be appreciated.

[0067]Referring now to FIG. 4, a graph of the relation between delivered
inspiratory time dTI, delivered expiratory time dTE, and forced
inhalation time TINH is depicted for a single breathing cycle for a
patient 12 undergoing pressure controlled mechanical ventilation (CMV).
As can be seen in the figure, the patient's 12 delivered inspiratory time
dTI is greater than the patient's 12 forced inhalation time
TINH, as can be viewed by the measured inspiratory time mTI.

[0068]Referring now to FIG. 5, a flowchart depicts a simplied arrangement
for setting the patient's 12 set inspiratory time sTI based on the
patient's 12 forced inhalation time TINH. More specifically, a
method begins in a step 100, during which the patient's 12 forced
inhalation time TINH is determined. Preferably, the patient's 12
forced inhalation time TINH is determined using the patient's 12
airway flow waveform, particularly when the first derivative thereof
approaches zero, as is well-known in the art. Alternatively, other
arrangements are also well-known in the art and can also be used to
determine the patient's 12 forced inhalation time TINH in step 100,
such as, for example, airway flow analysis of the patient 12; tidal
volume VT analysis of the patient 12; acoustic analysis of the
patient 12; vibration analysis of the patient 12; airway pressure
analysis Paw of the patient 12; capnographic morphology analysis of
the patient 12; respiratory mechanics analysis of the patient 12; and/or
thoracic excursion corresponding to gases exhaled from the lungs 30 of
the patient 12 (e.g., imaging the patient 12, plethysmographic analysis
of the patient 12, and/or electrical impedance tomography analysis of the
patient, and/or the like), etc.

[0069]Thereafter, the patient's 12 forced inhalation time TINH can be
used to set the patient's 12 set inspiratory time sTI on the
ventilator 16. More specifically, the patient's 12 set inspiratory time
sTI can be set based on the patient's 12 forced inhalation time
TINH, and, for example, set equal or substantively equal to the
patient's 12 forced inhalation time TINH, as shown in a step 102 in
FIG. 5, after which the method ends.

[0070]Now then, in accordance with the foregoing, the patient's 12 set
inspiratory time sTI is preferably set equal to, or slightly greater
than, the patient's 12 forced inhalation time TINH.

[0071]If, however, the patient's 12 forced inhalation flow does not cease,
or effectively decrease to an insignificant level so as not to add
substantive gas volume to the tidal volume VT, at the end of the
patient's 12 ventilated set inspiratory time sTI, as set by the
clinician and/or ventilator, then the clinician can increase the
patient's 12 set inspiratory time sTI until the patient's 12 forced
inhalation flow ceases, or effectively decreases to an insignificant
level.

[0072]As previously noted, the patient's 12 spontaneous breathing is
controlled by numerous reflexes that control the patient's 12 respiratory
rates f and tidal volumes VT. Particularly during pressure
controlled mechanical ventilation (CMV), however, these reflexes are
either obtunded and/or overwhelmed. In fact, one of the only aspects of
ventilation that usually remains under the patient's 12 control is the
patient's 12 forced inhalation time TINH, as required for a given
volume, as previously elaborated upon. This is why it can be used to set
the patient's 12 set inspiratory time sTI on the ventilator 16 based
thereon.

[0073]Now then, the inventive arrangements utilize the patient's 12 forced
inhalation time TINH and/or physiological parameters to determine
and/or set the patient's 12 set inspiratory time sTI, set expiratory
time sTE, and/or set tidal volume sVT, either directly and/or
indirectly. For example, the patient's 12 expiratory time TE may be
set directly, or may it be determined by the respiratory rate f for a
specific set inspiratory time sTI. Likewise, the patient's 12 set
tidal volume sVT may also be set directly, or it may be determined
by adjusting the patient's 12 inspiratory pressure (PINSP) in, for
example, pressure control ventilation (PCV). Adding the patient's 12 set
expiratory time sTE to the patient's 12 set inspiratory time
sTI results in a breath time that, when divided from 60 seconds,
produces the patient's 12 respiratory rate f. Accordingly, the patient's
12 set expiration time sTE, set inspiration time sTI, and
respiratory rate f may not be whole numbers.

[0074]Referring now to FIG. 6, a flowchart depicts a simplied arrangement
for setting the patient's 12 set inspiratory time sTI based on when
the patient's 12 forced inhalation flow ceases, or again effectively
decreases to an insignificant level during a pressure controlled
mechanical ventilation delivery mode or the like. More specifically, a
method begins in a step 104, during which the patient's 12 forced
inhalation flow cessation is determined, or at least effectively
decreased to an insignificant amount. Preferably, the patient's 12
effective forced inhalation flow cessation is determined using the
patient's 12 airway flow waveform, particularly when the first derivative
thereof approaches zero, as is well-known in the art. Alternatively,
other arrangements are also well-known in the art and can also be used to
determine when the patient's 12 effective forced inhalation flow ceases.

[0075]Thereafter, the patient's 12 effective cessation of forced
inhalation flow can be used to set the patient's 12 set inspiratory time
sTI on the ventilator 16. More specifically, the patient's 12 set
inspiratory time sTI can be set based on the patient's 12 effective
cessation of forced inhalation flow, and, for example, set equal or
substantively equal to when the patient's 12 effective forced inhalation
flow ceases, as shown in a step 106 in FIG. 6, after which the method
ends.

[0076]Referring now to FIG. 7, a flowchart depicts a simplied arrangement
for setting the patient's 12 set inspiratory time sTI based on when
the patient's 12 tidal volume VT is inspired, particularly during
pressure controlled mechanical ventilation. More specifically, a method
begins in a step 108, during which inspiration of the patient's 12 tidal
volume VT is determined. Preferably, the patient's 12 inspiration of
tidal volume VT is determined using a flow sensor. Alternatively,
other arrangements are also well-known in the art and can also be used to
determine when the patient's 12 tidal volume VT is inspired.

[0077]Thereafter, the patient's 12 inspiration of tidal volume VT can
be used to set the patient's 12 set inspiratory time sTI on the
ventilator 16. More specifically, the patient's 12 set inspiratory time
sTI can be set based on the patient's 12 inspiration of tidal volume
VT, and, for example, set equal or substantively equal to when the
patient's 12 tidal volume VT is inspired, as shown in a step 110 in
FIG. 7, after which the method ends.

[0078]As previously indicated,

f = 60 sT I + sT E I : E = sT I sT E

whereby knowing the patient's 12 respiratory rate f and I:E ratio allows
determining the patient's 12 set inspiratory time sTI and set
expiratory time sTE, while knowing the patient's 12 set inspiratory
time sTI and set expiratory time sTE conversely allows
determining the patient's 12 respiratory rate f and I:E ratio.
Preferably, the clinician and/or the ventilator sets the patient's 12
respiratory rate f and set inspiratory time sTI, for which the
patient's 12 set expiratory time sTE and I:E ratio can then be
determined using the above equations.

[0079]While various mandatory mechanical ventilation modes can be used
with the inventive techniques, volume guaranteed pressure control
ventilation (i.e., PCV-VG), in particular, will be further described
below as a representative example, as it has a decelerating flow profile
based on the patient's forced inhalation in response to the ventilator
delivered inspiratory pressure, and the set tidal volume sVT is
guaranteed by the ventilator on a breath-to-breath basis. However, the
inventive arrangements are also equally applicable to other pressure
control ventilation (PCV) modes. In any event, several of the primary
control settings on a typical ventilator 16 include controls for one or
more of the following: set expiratory time sTE, set inspiratory time
sTI, set tidal volumes sVT, and/or fraction of inspired oxygen
FIO2.

[0080]Now then, according to the patient's 12 physiological measurements
in a steady state condition: [0081]V O2=FETCO2*MVA
wherein V O2 is the volume of CO2 per minute exhaled by the
patient 12 and MV is the minute volume, which is a total volume exhaled
per minute by the patient 12. As used in these expressions, a subscripted
A indicates "alveolar," which is a part of the patient's 12 lungs 30 that
participate in gas exchanges with the patient's 12 blood, in contrast to
deadspace (VD), such as the patient's 12 airway.

[0082]In this steady state condition and over a short duration, the
patient's 12 blood reservoir is such that V O2 is a constant (blood
reservoir effects will be elaborated upon below), and, in accordance with
this equation, as MVA increases, the patient's 12 end tidal carbon
dioxide FETCO2 decreases for a constant V O2. Accordingly,
substituting MVA=VA*f yields the following:

[0083]Accordingly, the same V O2 can be achieved by increasing the
patient's 12 VA and/or decreasing the patient's 12 respiratory rate
f Decreasing the patient's 12 respiratory rate f has the same effect as
increasing the patient's 12 delivered expiratory time dTE on the
ventilator 16. In fact, numerous respiratory rate f and delivered
expiratory time dTE combinations can result in equivalent or nearly
equivalent V O2 production. Accordingly, an optional combination is
desired.

[0084]As previously described, the patient's 12 forced inhalation time
TINH measures the time period when the patient's 12 forced
inspiratory gas flow ceases during pressure controlled mechanical
ventilation--i.e., the patient's 12 forced inhalation time TINH
comprises the duration of gas flow during the patient's 12 delivered
inspiratory time dTI. A cessation of flow indicates that the
patient's 12 lungs 30 are at their end-inspired lung volume (EILV),
subtended by the end-inspired airway pressure. Continued gas exchange
beyond EILV could become less efficient, largely as a result of the
completion of inspired volume of gases in the patient's 12 lungs 30, and
the gases would likely have mixed with the gases already in the patient's
12 lungs 30 since the last exhaled breath.

[0085]Referring now to FIG. 8, the clinician can also increase or decrease
the patient's 12 set expiratory time sTE on the ventilator 16 until
the patient's 12 resulting end tidal carbon dioxide FETCO2 is
or becomes stable to changes in the patient's 12 delivered expiratory
time dTE. More specifically, this will identify the patient's 12
optimal expiratory time TE-OPTIMAL. Preferably, the clinician and/or
ventilator 16 will be able to determine this optimal expiratory time
TE-OPTIMAL within a few breaths of the patient 12 for any given
inspiratory cycle. For example, when a stable end tidal carbon dioxide
FETCO2 is reached, then preferred equilibration of carbon
dioxide CO2 during a given delivered expiratory time dTE can be
achieved, as little or no more carbon dioxide CO2 can be effectively
extracted from the patient's 12 blood by further increasing the patient's
12 delivered expiratory time dTE. Accordingly, the patient's 12
optimal expiratory time TE-OPTIMAL can then be ascertained and/or
set.

[0086]More specifically, the patient's 12 end tidal carbon dioxide
FETCO2 can be considered stable or more stable at or after a
point A on a dTE response curve 150 in the figure (e.g., see a first
portion 150a of the dTE Response Curve 150) and non-stable or less
stable or instable at or before that point A (e.g., see a second portion
150b of the dTE Response Curve 150). Accordingly, the point A on the
dTE Response Curve 150 can be used to determine the patient's 12
optimal expiratory time TE-OPTIMAL, as indicated in the figure.

[0087]Physiologically, when the patient's 12 end tidal carbon dioxide
FETCO2 is equal to the patient's 12 capillary carbon dioxide
FcCO2, diffusion stops and carbon dioxide CO2 extraction from
the patient's 12 blood ceases. Ideally, the patient's 12 optimal
expiratory time TE-OPTIMAL is set where this diffusion becomes
ineffective or stops. Otherwise, a smaller delivered expiratory time
dTE could suggest that additional carbon dioxide CO2 could be
effectively removed from the patient's 12 blood, while a larger delivered
expiratory time dTE could suggest that no additional carbon dioxide
CO2 could be effectively removed from the patient's 12 blood.

[0088]Preferably, finding the patient's 12 stable end tidal carbon dioxide
FETCO2 occurs without interference from the patient's 12 blood
chemistry sequelae. A preferred technique for finding the patient's 12
stable end tidal carbon dioxide FETCO2 can increase or decrease
the patient's 12 expiratory time dTE, which may minimally disrupt
the patient's 12 blood reservoir of carbon dioxide CO2. Changes in
the patient's 12 delivered expiratory time dTE will affect how the
patient's 12 blood buffers the patient's 12 carbon dioxide CO2, and
if that blood circulates back to the patient's 12 lungs 30 before the
patient's 12 set expiratory time sTE is optimized, then the
patient's 12 end tidal carbon dioxide FETCO2 will be different
for a given expiratory time dTE. At that point, optimizing the
patient's 12 set expiratory time sTE may become a dynamic process.
In any event, the time available to find the patient's 12 optimal
expiratory time TE-OPTIMAL may be approximately one (1) minute for
an average adult patient 12.

[0089]One way to decrease the likelihood of interference from the
patient's 12 blood chemistry sequelae is to change the patient's 12
delivered expiratory time dTE for two (2) or more expirations, and
then use the patient's 12 resulting end tidal carbon dioxide
FETCO2 to extrapolate using an apriori function, such as an
exponential function, by techniques known in the art.

[0090]For example, if the patient's 12 first end tidal carbon dioxide
FETCO2 was originally determined at a point B on a dTE
response curve 152 in the figure, and then at a point C, and then at a
point D, and then at a point E, and then at a point F, and then at a
point G, and then so on, then the data points (e.g., points B-G) could be
collected and a best fit dTE response curve 152 obtained;
extrapolating as needed. Preferably, the dTE response curve 152 is
piecewise continuous. For example, a first portion 152a of the dTE
response curve 152 may comprise a stable horizontal or substantially
horizontal portion (e.g., points B-D) while a second portion 152b thereof
may comprise a polynomial portion (e.g., points E-G). Where this first
portion 152a and second portion 152b of the dTE response curve 152
intersect (e.g., see point A on the dTE response curve 152) can be
used to determine the patient's 12 optimal expiratory time
TE-OPTIMAL, as indicated in the figure.

[0091]For example, referring now to FIG. 9, an arrangement to identify the
patient's 12 optimal expiratory time TE-OPTIMAL based on an
iterative process will be described. More specifically, one preferred
arrangement for determining an optimal expiratory time TE-OPTIMAL
collects FETCO2 data in equal or substantially equal expiratory
time increments ΔTE. For example, if the patient's 12 first
end tidal carbon dioxide FETCO2 was originally determined to be
within the first portion 152a of the dTE response curve 152 (e.g.,
see points B-D), then the clinician and/or ventilator 16 could decrease
the patient's 12 delivered expiratory times dTE until the patient's
12 end tidal carbon dioxide FETCO2 readings were within the
second portion 152b of the dTE response curve 152 (e.g., see points
E-G).

[0092]For example, if the patient's 12 end tidal carbon dioxide
FETCO2 was originally determined to be at point C on the
dTE response curve 152 (i.e., within the first portion 152a of the
dTE Response Curve 152), then the patient's 12 delivered expiratory
time dTE could be decreased until the patient's 12 next end tidal
carbon dioxide FETCO2 was determined to be at point D on the
dTE response curve 152, at which point the patient's 12 end tidal
carbon dioxide FETCO2 would still be determined to be within
the first portion 152a of the dTE response curve 152. Accordingly,
the patient's 12 delivered inspiratory time dTI could be decreased
again until the patient's 12 next end tidal carbon dioxide
FETCO2 was determined to be at point E on the dTE response
curve 152, at which point the patient's 12 end tidal carbon dioxide
FETCO2 would now be determined to be within the second portion
152b of the dTE response curve 152 (i.e., the patient's 12 end tidal
carbon dioxide FETCO2 would have dropped and thus not be at the
patient's 12 optimal expiratory time TE-OPTIMAL). Accordingly, a
smaller delivered expiratory time increment ΔTE/x could be
made to determine when the patient's 12 end tidal carbon dioxide
FETCO2 was as at point A on the dTE response curve
152--i.e., at the intersection of the first portion 152a of the dTE
response curve 152 and the second portion 152b of the dTI response
curve 152. In this iterative fashion, successively smaller delivered time
increments and/or decrements ΔTE are made to determine the
patient's 12 optimal expiratory time TE-OPTIMAL, as indicated in the
figure.

[0093]In like fashion, if the patient's 12 end tidal carbon dioxide
FETCO2 was originally determined to be at point F on the
dTE response curve 152 (i.e., within the second portion 152b of the
dTE response curve 152), then the patient's 12 delivered expiratory
time dTE could be increased until the patient's 12 next end tidal
carbon dioxide FETCO2 was determined to be at point E on the
dTE response curve 152, at which point the patient's 12 end tidal
carbon dioxide FETCO2 would still be determined to be within
the second portion 152b of the dTE response curve 152. Accordingly,
the patient's 12 delivered expiratory time dTE could be increased
again until the patient's 12 next end tidal carbon dioxide
FETCO2 was determined to be at point D on the dTE response
curve 152, at which point the patient's 12 end tidal carbon dioxide
FETCO2 would now be determined to be within the first portion
152a of the dTE response curve 152 (i.e., the patient's 12 end tidal
carbon dioxide FETCO2 would not have increased and thus not be
at the patient's 12 optimal expiratory time TE-OPTIMAL).
Accordingly, a smaller delivered expiratory time decrement
ΔTE/x could be made to determine when the patient's 12 end
tidal carbon dioxide FETCO2 was as at point A on the dTE
response curve 152--i.e., at the intersection of the first portion 152a
of the dTE response curve 152 and the second portion 152b of the
dTE response curve 152. In this iterative fashion, successively
smaller delivered time increments and/or decrements ΔTE are
again made to determine the patient's 12 optimal expiratory time
TE-OPTIMAL, as indicated in the figure.

[0094]In addition, once the patient's 12 optimal expiratory time
TE-OPTIMAL is determined, it is realized this may be dynamic, by
which the above arrangements can be repeated, as needed and/or desired.

[0095]Now then, a lower bound on the patient's 12 set expiratory time
sTE should be directly related to the minimal time required for the
patient 12 to exhale the delivered tidal volume dVT.

[0096]A lower bound for the patient's 12 set and delivered tidal volume
sVT, dVT should exceed VD, preferably within a
predetermined and/or clinician-selected safety margin. Preferably, a
re-arrangement of the Enghoff-Bohr equation can be used to find VD
or the following variation:

V D = V T - V A = V T - V CO 2 F ET CO 2

[0097]After the patient's 12 end tidal carbon dioxide FETCO2 is
determined, then the patient's 12 set tidal volume sVT can be set
accordingly, but it may not yet be set at an optimal value. Often, the
clinician and/or ventilator 16 will attempt to determine this desired
value. For example, the clinician may consider the desired value as the
patient's 12 pre-induction end tidal carbon dioxide FETCO2. The
clinician can then adjust the patient's 12 set tidal volume sVT
until the desired end tidal carbon dioxide FETCO2 is achieved.
Alternatively, or in conjunction therewith, a predetermined methodology
can also be used to adjust the patient's 12 delivered tidal volume
dVT until the desired end tidal carbon dioxide FETCO2 is
achieved. For example, such a methodology may use a linear method to
achieve a desired end tidal carbon dioxide FETCO2.

[0098]Preferably, the clinician can be presented with a dialog box on the
monitor 38, for example (see FIG. 1), indicating the current and/or
updated optimal ventilator 16 settings to be accepted or rejected.
Preferably, the settings can be presented to the clinician in the dialog
box for acceptance or rejection, who can then accept them, reject them,
and/or alter them before accepting them. Alternatively, the settings can
also be automatically accepted, without employing such a dialog box.

[0099]As previously indicated, different techniques can also be used to
search for optimal settings for the ventilator 16. If desired, the
delivered values can also be periodically altered to assess whether, for
example, the settings are still optimal. Preferably, these alterations
can follow one or more of the methodologies outlined above, and they can
be determined based on a predetermined and/or clinician-selected time
interval, on demand by the physiological, and/or determined by other
control parameters, based, for example, on clinical events, such as
changes in the patient's 12 end tidal carbon dioxide FETCO2, or
on clinical events such as changes in drug dosages, repositioning the
patient, surgical events and the like. For example, the patient's 12
delivered expiratory time dTE can vary about its current value set
expiratory time sTE and the resulting end tidal carbon dioxide
FETCO2 can be compared to the current end tidal carbon dioxide
FETCO2 to assess the optimality of the current settings. If,
for example, a larger delivered expiratory time dTE leads to a
larger end tidal carbon dioxide FETCO2, then the current set
expiratory time sTE could be too small.

[0100]In an alternative embodiment, the dTE response curve 154 could
be expressed in terms of VCO2 instead of FETCO2, as shown
in FIG. 10. The morphology of the response curve 154 will be similar to
that as shown in FIG. 9. Without loss of generality, the above techniques
can be used to find TE-OPTIMAL utilizing VCO2 as opposed to
FETCO2. The VCO2 is equal to the inner product over one
breath between a volume curve and a CO2 curve. The flow and CO2
curves should be synchronized in time.

[0101]One representative summary of potential inputs to, and outputs from,
such a methodology is depicted below:

[0102]In addition, by more closely aligning the patient's 12 set
inspiratory time sTI and the patient's 12 forced inhalation time
TINH during mandatory mechanical ventilation, mean alveolar
ventilation increases. In addition, there is additional optimal carbon
dioxide CO2 removal, improved oxygenation, and/or more anesthesia
agent equilibration, whereby ventilated gas exchanges become more
efficient with respect to use of lower set tidal volume sVT compared
to conventional settings. Minute ventilations and respiratory resistance
can be reduced, and reducing volumes can decrease the patient's 12 airway
pressure Paw thereby reducing the risk of inadvertently over
distending the lung.

[0103]In addition, the inventive arrangements facilitate ventilation for
patients 12 with acute respiratory distress syndrome, and they can be
used to improve usability during both single and double lung
ventilations, as well transitions therebetween.

[0104]As a result of the foregoing, several of the inventive arrangements
set the patient's 12 set inspiratory time sTI equal to the time
period between when the ventilator 16 permits the patient 12 to inhale
and when the patient's 12 inspiratory flow ceases--i.e., the patient's 12
forced inhalation time TINH. This facilitates the patient's 12
breathing by ensuring that ventilated airflows are appropriate for that
patient 12 at that time in the treatment. In addition, methods of setting
optimal patient expired time TE-OPTIMAL and desired tidal volume
VT are presented.

[0105]It should be readily apparent that this specification describes
illustrative, exemplary, representative, and non-limiting embodiments of
the inventive arrangements. Accordingly, the scope of the inventive
arrangements are not limited to any of these embodiments. Rather, various
details and features of the embodiments were disclosed as required. Thus,
many changes and modifications--as readily apparent to those skilled in
these arts--are within the scope of the inventive arrangements without
departing from the spirit hereof, and the inventive arrangements are
inclusive thereof. Accordingly, to apprise the public of the scope and
spirit of the inventive arrangements, the following claims are made: